FIG. 2 is a cross-sectional view of a perpendicular magnetic recording medium 200 according to related art. The medium 200 includes a substrate 202, and an adhesion layer 204 formed on the substrate 202. As illustrated, the medium 200 also includes a pair of soft under-layers 206, 210 with a spacer layer 208 formed therebetween. FIG. 2 also illustrates that a seed layer 212 is formed on the upper soft-underlayer 210, and a pair of intermediate layers 214, 216 formed on the seed layer 212. Further, a non-magnetic granular layer 218 is formed on the upper intermediate layer 216 to allow the growth of one or more recording layer units 236, 238, 240.
As illustrated, three recording layer units 236, 238, 240 are provided in the medium 200. The lower recording layer unit 236 includes a lower magnetic layer 220 formed on the non-magnetic granular layer 218 and a lower exchange breaking layer 222 formed on the lower magnetic layer 220. The middle recording layer unit 238 includes a middle magnetic layer 224 formed on the lower exchange breaking layer 222 and a middle exchange breaking layer 226 formed on the middle magnetic layer 224. The upper recording layer unit 240 includes an upper magnetic layer 226 formed on the middle exchange breaking layer 226 and an upper exchange breaking layer 230 formed on the upper magnetic layer 228. A metallic CAP layer 232 is formed on the upper exchange breaking layer 232 and a protective carbon overcoat layer 234 is formed on the metallic CAP layer 232.
In the related art storage medium 200 of FIG. 2, each of the magnetic layers 220, 224, 228 is formed from a magnetic alloy containing one or more of Cobalt (Co), Platinum (Pt), and Chromium (Cr) and grain boundary segregation materials formed from one or more of Silicon Oxide (SiO2), Chromium Oxide (Cr2O3), and Cobalt Oxide (CoO). Each of the magnetic layers 220, 224, 228 may also include Boron (B) and/or Ruthenium (Ru). Further, the lower and middle exchange breaking layers 222 and 226 are formed from an alloy of Co and Cr and grain boundary segregation materials formed from Titanium Oxide (TiO2). Additionally, the upper exchange blocking layer 230 may be formed from an alloy containing Co and Ru.
The continued demand for Hard Disk Drives (HDD) with lower cost and larger capacity has driven the production of media, such as that illustrated in FIG. 2, which have higher areal density. However, in media such as that illustrated in FIG. 2, the physical limitation of write-head field strengths can restrict improvements in the Signal to Noise Ratio (SNR) required to maintain the higher areal density. Specifically, as grain size is reduced to improve SNR, it becomes necessary to increase magnetic field strength during magnetic reversal (i.e. the anisotropy field) of each grain in order to secure thermal stability for longer duration storage of recoded bits.
There is therefore a need for an improved disk media material that that may realize improved SNR and a higher thermal stability factor without sacrificing writability.